Embodiments of the present invention relate to the registration of an electron beam pattern on a substrate.
An electron beam apparatus is capable of scanning one or more electron beams onto a substrate to register an electron beam pattern in electron-sensitive material on the substrate. A typical electron beam apparatus comprises a vacuum chamber comprising electron source, modulating, and detecting components. The electron source components generate electrons which are modulated and scanned across the substrate to register the electron beam pattern on the substrate. The electron beam may also be detected to determine the beam position relative to the substrate.
One commonly used electron source comprises a field-emission electron source. These sources have a conducting cathode with a tapered tip that is powered with a negative voltage relative to a nearby conducting anode. A resistor coil placed behind the tip may be provided to resistively heat the tip to thermally assist in the emission of electrons from the tip. However, conventional resistor coils typically radiate heat omnidirectionally and often only a small portion of the heat is actually transferred to the cathode tip. Thus, conventional resistor coils do not provide a very efficient method of heating the cathode tip. Also, the escaped heat may undesirably heat the walls and other components of the vacuum chamber. Additionally, the wires that carry power to the resistor coil can also pose a short-circuiting risk or can cause electrical or magnetic interference with other components inside the vacuum chamber.
An alternative electron source comprises a laser beam which is directed sideways onto the surface of the cathode tip, as disclosed in U.S. Pat. No. 3,864,572, which is incorporated herein by reference in its entirety. However, in this electron source, the cathode tip is heated non-uniformly because the laser beam illuminates only one side of the tip. Additionally, a portion of the laser beam is reflected off the tip, thereby reducing the heating efficiency. Furthermore, because the tip is small and tapered, it is difficult to align the laser beam to the tip, and the laser beam may be sometimes mis-directed. Still furthermore, the size and shape of this electron source makes it difficult to array in an electron beam apparatus. As a result, the electron source does not efficiently emit electrons and may also provide an inconsistent electron stream.
Thus, it is desirable to have an electron beam apparatus and electron source capable of efficiently heating an electron emitting cathode to generate a stream of electrons. It is also desirable for the electron beam apparatus to provide a reliable and consistent electron current during operation.
An electron source comprises an anode; a cathode comprising an electron emitting portion and having a cathode axis; an electromagnetic radiation source adapted to generate an electromagnetic radiation beam to heat the cathode; and a lens adapted to direct the electromagnetic radiation beam onto the cathode, the lens having a lens axis that forms an acute angle with, or is substantially parallel to, the cathode axis.
An electron beam apparatus to register an electron beam pattern on a substrate comprises a vacuum chamber; a substrate support to support a substrate; an electron source to provide an electron beam in the vacuum chamber, the electron source comprising (a) an anode, (b) a cathode comprising an electron emitting portion and having a cathode axis, (c) an electromagnetic radiation source adapted to generate an electromagnetic radiation beam to heat the cathode, and (d) a lens adapted to direct the electromagnetic radiation beam onto the cathode, the lens having a lens axis that forms an acute angle with, or is substantially parallel to, the cathode axis; and an electron beam modulator and scanner to modulate and scan the electron beam across the substrate to register an electron beam pattern on the substrate.
A method of generating electrons from an electron source comprising an anode, and a cathode having an electron emitting portion and a cathode axis comprises (a) negatively biasing the cathode relative to the anode; and (b) directing an electromagnetic radiation beam onto the cathode at an acute angle with, or substantially parallel to, the cathode axis.
An electron source comprises an anode; a cathode comprising an electron emitting portion having a tip, a beam-receiving portion, and a cathode axis; a laser beam source adapted to generate a laser beam to heat the cathode; and a lens adapted to focus the laser beam onto the cathode, the lens being supported by a rod that is substantially parallel to the cathode axis and terminates in the electron emitting portion of the cathode.
A method of registering an electron beam pattern on a substrate comprises (a) placing a substrate on a substrate support; (b) generating an electron beam by (i) biasing a cathode relative to an anode, and (ii) generating an electromagnetic radiation beam and directing the electromagnetic radiation beam onto the cathode to heat the cathode; and (c) modulating and scanning the electron beam across the substrate to register an electron beam pattern on the substrate.